Editing Otto Hahn (section)

===Rubidium–strontium dating===
While Hahn was in North America in 1905–1906, his attention had been drawn to a mica-like mineral from [[Manitoba]] that contained [[rubidium]]. He had studied the radioactive decay of [[rubidium-87]], and had estimated its half-life at 2 x 10<sup>11</sup> years. It occurred to him that by comparing the quantity of strontium in the mineral (which had once been rubidium) with that of the remaining rubidium, he could measure the age of the mineral, assuming that his original calculation of the half-life was reasonably accurate. This would be a superior dating method to studying the decay of uranium, because some of the uranium turns into helium, which then escapes, resulting in rocks appearing to be younger than they really were. [[Jacob Papish]] helped Hahn obtain several kilograms of the mineral.{{sfn|Hahn|1966|pp=85–88}}

In 1937, Strassmann and Ernst Walling extracted 253.4 milligrams of strontium carbonate from 1,012 grams of the mineral, all of which was the [[strontium-87]] isotope, indicating that it had all been produced from radioactive decay of rubidium-87. The age of the mineral had been estimated at 1,975 million years from uranium minerals in the same deposit, which implied that the half-life of rubidium-87 was 2.3 x 10<sup>11</sup> years: quite close to Hahn's original calculation.<ref>{{cite journal |last1=Hahn |first1=O. |last2=Strassman |first2=F. |last3=Walling |first3=E. |title=Herstellung wägbaren Mengen des Strontiumisotops 87 als Umwandlungsprodukt des Rubidiums aus einem kanadischen Glimmer |trans-title=Production of Weighable Amounts of the Strontium Isotope 87 as a Conversion Product of Rubidium from Canadian Mica |language=de |journal=Naturwissenschaften |issn=0028-1042 |volume=25 |issue=12 |date=19 March 1937 |page=189 |doi=10.1007/BF01492269 |bibcode=1937NW.....25..189H |doi-access=free }}</ref><ref>{{cite journal |last1=Hahn |first1=O. |last2=Walling |first2=E. |title=Über die Möglichkeit geologischer Alterbestimmung rubidiumhaltiger Mineralen und Gesteine |trans-title=On the Possibility of Geological Age Determination of Minerals and Rocks Containing Rubidium |language=de  |journal=Zeitschrift für anorganische und allgemeine Chemie |issn=0044-2313 |volume=236 |issue=1 |date=12 March 1938 |pages=78–82 |doi=10.1002/zaac.19382360109 }}</ref> [[Rubidium–strontium dating]] became a widely used technique for dating rocks in the 1950s, when [[mass spectrometry]] became common.{{sfn|Bowen|1994|pp=162–163}}